1. Field of the Invention
The present invention relates to an apparatus for automatically adjusting a direction of a light axis of a vehicle headlight.
2. Description of the Background Art
Automatically adjusting a direction of a light axis of a vehicle headlight is known as disclosed in Japanese Patent Application Laid-Open No. 2000-142213. This document describes a technique for automatically adjusting a direction of a light axis of a vehicle headlight in accordance with an output of a single vehicle-height sensor while taking account of variable load conditions.
To be more specific, this technique uses an approximating curve divided into an occupant-load region and a trunk-load region in order to estimate an inclination of the light axis of the vehicle headlight to the horizontal plane for each of two different load conditions. That is because the amount and direction of the inclination of the light axis of the vehicle headlight to the horizontal plane varies differently depending on the load conditions (occupant load, trunk load, or combination of them). So, the approximating curve is constituted by two straight line segments having different slopes corresponding to the occupant-load region and the trunk-load region respectively.
The slope of the straight line segment in the trunk-load region is steeper than that of the straight line segment in the occupant-load region. However, this technique has a problem in that the difference between the pitch angle corresponding to the inclination of the light axis of the vehicle headlight to the horizontal plane estimated on the basis of the output of the vehicle-height sensor and the actual pitch angle becomes large when the vehicle is under the trunk-load condition, especially when the vehicle is nearly fully loaded, and all the seats of the vehicle are occupied, which may cause a large error to occur in adjusting the direction of the light axis of the vehicle headlight on the basis of the estimated pitch angle.
Incidentally, it is also known to switch between two approximating curves having different slopes depending on whether the front passenger's seat is occupied or not for estimating the pitch angle. However, in this case, since a seat sensor for sensing presence of a passenger and a circuit relevant to this seat sensor are required, the production costs are increased.